This invention relates generally to telecommunication systems, and more particularly to determination of the points of origin of error conditions and failures in a telecommunication system.
A digital telecommunication system that connects users in disparate locations can be logically divided into various regions of equipment. Each equipment region carries with it an accompanying responsibility for maintenance and repair of that equipment. A telecommunication system typically includes at least one customer premises equipment (CPE) region, which includes telecommunication equipment that is generally maintained by a customer such as a business establishment. A second region typically includes equipment that is maintained by a local exchange carrier (LEC) and a third region typically includes equipment that is maintained by an inter-exchange carrier (IEC). The LEC equipment and IEC equipment can be collectively referred to as the network equipment.
A CPE region can include a variety of telecommunications equipment, such as telephones, facsimile machines, computers, and modems carrying a variety of data signals. The CPE region is typically linked to the LEC, which provides communication services to a plurality of CPE regions. The LEC is commonly referred to or viewed as the “local telephone company” of the CPE business. Several LECs are then communicatively linked by one or more IECs, for example, IECs such as “AT&T”, “MCI/Worldcom”, and “Sprint.” These carriers are often referred to as “long distance” carriers. It is generally the responsibility of each entity or region to maintain its own equipment. For example, the customer has the responsibility of maintaining its communication equipment and ensuring that its equipment transmits a proper signal. Likewise, the LEC has the responsibility of maintaining equipment that is outside the boundary of the customer but not at the level of the long distance carrier (IEC).
The customer and local exchange carriers use maintenance equipment, such as a DS1 Interface Connector or network interface unit (NIU) (hereafter referred to as “network interface unit” or NIU) and a channel service unit (CSU), that assist in performing test and maintenance functions for the respective telecommunication equipment and connecting lines. The maintenance equipment generates maintenance signals that have an alarm state that indicates whether an error condition or a failure is present on an incoming or outgoing signal.
In accordance with standards such as the Standard T1.403-1999, one type of maintenance signal alarm indication is the Remote Alarm Indicator (RAI), which is an indication provided to a source device indicating a signal failure condition at a device that is configured to receive the signal. An NIU or CSU transmits the RAI signal in the outgoing direction when an incoming signal is lost. Another type of alarm indication, under Standard T1.403-1999, is the Alarm Indication Signal (AIS), which is a signal transmitted in place of a “normal” data signal to maintain transmission continuity and to indicate to a receiving terminal that there is a transmission fault located either at or upstream (i.e., relative to the flow of data) from the equipment originating the AIS signal. According to the Standard T1.403-1999, the AIS signal is generated as an unframed, all-ones signal.
There currently exist network interface units (NIUs) that are configured to receive and decode digital signals, such as the maintenance signals generated by the CSUs discussed above. In particular, signals called “DS1” are signals transmitted by an NIU at a nominal rate of 1.544 Mbits per second in accordance with the Standard T1.403-1999 referred to above. The NIUs are located at the point of demarcation between the CPE and the LEC equipment. The NIUs are used to determine the point of origin of alarm indication signals and thereby determine whether the customer, the LEC, or the IEC is responsible for attending to the condition that caused the alarm. The DS1 signal configuration includes a variant of AIS referred to as AIS-Customer Installation (AIS-CI), which is generated within the network and is transmitted toward the network, away from the customer installation, when either an AIS defect or an LOS defect has been detected in the signal received from the CI. RAI-CI signal is a variant of the RAI, which indicates that RAI has been detected in the signal from the CI and that the defect or failure that caused the origination of the RAI is not found in the signal from the network.
Other signal configurations have been proposed and are being used, such as the “DS3” signal specified by the Standard T1.107-2001. A DS3 signal comprises a “layering” or “multiplexing” of multiple DS1 signals and has frame structures, payload, header bits, and the like of a different configuration from the DS1 signals described above. Thus, according to the Standard T1.107-2001, all DS3 signals should be framed. Accordingly, a network interface unit that is transmitting DS3 signals cannot indicate the location of alarm events using the above-referenced DS1 maintenance signals scheme because the alarm indicators for these signals are unframed. This makes it difficult to trouble shoot problems in communications between the CPE, LEC, and IEC regions, increasing maintenance costs. That is, a network interface device that can recognize DS1 maintenance signals cannot necessarily recognize DS3 maintenance signals. For example, a network interface device that recognizes AIS-CI signals in the DS1 format will detect the AIS-CI pattern in the signal data comprising a repeating 16-bit pattern including eight zero-bits followed by eight one-bits. This type of processing will not detect corresponding DS3 signals. Furthermore, the form of the DS1 RAI-CI signal cannot be used for DS3 because the RAI signal for DS3 has a format different from that of DS1 RAI.
There is therefore a need in the art for configuring DS3 maintenance signals that can be recognized by the network interface device.